Certain medical procedures, such as, for example, contrast media injections during cardiological procedures, can require that liquids (such as radiographic contrast agents in, for example, angiography) be injected into a patient's system under high pressures. Such pressures are commonly as high as 1200 lb/in2 (psi) or more than 60,000 mm Hg. While performing such procedures it is also desirable to measure the patient's biological pressures. For example, in angiography it is desirable to record the much lower intravascular and intracardiac pressures—generally falling within the range of −1 to +6 psi—between high pressure injections of the contrast media. Generally, pressure transducers that are designed for physiological measurements cannot tolerate even moderate injection pressures and therefore must be isolated from the fluid path during a high-pressure injection. One such method of isolating pressure transducers is described in U.S. Pat. No. 5,800,397 (Wilson et al.), that uses a manifold to isolate a low pressure system line—where a pressure transducer can be located—from a high pressure contrast medium injection line based on a spool valve concept.
Spool-type manifolds are common in industrial applications and can manage very high pressures. However, such manifolds also require close manufacturing tolerances, are generally expensive, and are designed for use in permanent installations. Also, due to its mechanical “stickiness”, the position (open/closed) of a spool-type manifold needs to be monitored by a sensor to avoid malfunction with insipation of blood during a syringe refill. In medical applications, plastic and elastomeric parts are commonly used. This is because pressures are generally low in such environments and sterile parts need to be inexpensive so that for hygienic and safety reasons they can be readily disposed of after a single use. Such polymers have a drawback; they are less conducive to a consistent fit between different parts, which tends to decrease reliability. No device currently exists that combines low cost and ease of manufacture and use with the high pressure capability of industrial valves.
In addition, devices adapted to measure high pressures which would, by definition, be capable of withstanding those pressures, are simply not sensitive enough to accurately measure physiological pressures. Thus, in the example discussed above, a physician performing an angiography using only a high-pressure sensor could, in fact, monitor the injection pressure while contrast material is being injected, but would have no way of monitoring the patient's blood pressure when no injection is occurring. Thus, what is needed in the art is a method of facilitating the deployment of pressure measuring devices—that is sensitive enough to measure physiological pressures—within high fluid pressure environments in a manner that either isolates or protects such devices when high pressures are present.
Thus, within the objects of the present invention are methods, apparatus and systems which facilitate placing devices that make accurate physiological pressure measurements within environments that are intermittently subjected to high pressure fluid flow.